1. Field of the Invention
The present invention relates to a method and apparatus for the analysis of a liquid carrying a suspension of organic matter. The invention is particularly directed towards an ozone hydroxyl radical analysis method of the type utilising ozone and generally comprising the steps of:
sampling the liquid;
delivering the sample to the reactor vessel;
adding an acid to lower the pH;
stripping off inorganic carbon as carbon dioxide to give a value for total inorganic carbon present;
using a base liquid having hydroxyl ions to increase the pH;
adding ozone through a reactor inlet to form hydroxyl radicals and thus ensure effective oxidation;
cutting off the ozone;
lowering the pH of the sample; and
stripping off carbon dioxide to give a value of total organic carbon present.
2. Background Information
Ideally any analyser should be able to sequentially analyse samples from a number of different location.
Preferably any such analyser should be able to measure total organic carbon, total inorganic carbon, total carbon and after correlation, chemical oxygen demand (COD) and biochemical oxygen demand (BOD).
As mentioned above, the analysers of the type which the present invention is concerned, is to use the principle that ozone can be used to produce free hydroxyl radicals. The radicals will oxidise the organic material they come in contact with and produce carbon dioxide. When the pH is lowered, the gas is stripped off with oxygen or any other stripping gas such as air which does not itself contain carbon dioxide e.g. air nitrogen, etc. and the amount of carbon dioxide is measured with a carbon dioxide detector. Then a clear measure of total organic carbon is obtained.
Any analyser should have low chemical usage costs and a good oxidation of both dissolved organic material and particulates. Efficient ozone generation is vital.
It is also essential that good control devices be used to ensure that the system operates correctly.
The present invention is directed towards providing an improvement in such an analysis method and to provide an improved construction of reactor vessel and apparatus for carrying out such a method and in particular to providing an improved construction of ozone generator.
According to the invention there is provided an ozone hydroxyl radical analysis method for a liquid carrying a suspension of organic matter of the type utilising ozone in an analyser including a reactor vessel and a plurality of fluid inlet and outlet valves comprising the steps of:
sampling the liquid;
delivering the sample to the reactor vessel;
adding an acid to lower the pH;
stripping off inorganic carbon as carbon dioxide to give a value for total inorganic carbon present;
using a base liquid having hydroxyl ions to increase the pH;
adding ozone through a reactor inlet to from hydroxy radicals and thus ensure effective oxidation;
cutting off the ozone;
lowering the pH of the sample; and
stripping off carbon dioxide to give a value of total organic carbon present, and;
prior to carrying out the method the initial stop is performed of:
introducing beads of an inert material into the reactor vessel; and
periodically the step is performed of introducing a metallic catalyst into the reactor vessel to coat the beads.
The use of beads of an inert material has been found to be particularly effective when combined with a metallic catalyst.
Ideally the catalyst is introduced into the reactor vessel each time a liquid sample is delivered into the reactor vessel. Particularly suitable forms of metallic catalysts are manganese, cobalt, nickel, silver, lead and molybdenum.
Ideally the beads are glass beads and the catalyst is manganese. The beads are substantially spherical having a diameter of between 1 mm and 10 mm and more preferably between 2.5 mm and 3.5 mm.
The ozone concentration can be between 1% and 25% by volume and is generally greater than 8% by volume.
The base liquid is a concentrated Source of hydroxy ions of between 0.25 and 10 molar, generally greater than 1 molar and preferably greater than 1.2 molar and the base liquid is chosen from sodium hydroxide or potassium hydroxide.
Ideally the sample, acid, base liquid and ozone mixture are recirculated through the reactor vessel and ideally the inlet used to deliver ozone into the reactor vessel is washed periodically by an acid and this acid is often that used to lower the pH.
Ideally in each reaction is carried out an initial detection step is carried out to ascertain if carbon dioxide gas is given off and in the event of the level of carbon dioxide detected falling below a pre-set level, the test is abandoned until the malfunction is corrected.
In this latter method the pre-set level is determined by introducing the acid and base liquid into the reactor vessel and measuring the resultant carbon dioxide released.
In a method according to the invention when the total inorganic carbon is being detected the test is continued until the flow of carbon dioxide ceases.
Further an automatic leak test is performed periodically by:
closing all outlet valves from the reactor vessel;
delivering a gas into the reactor vessel at a fixed rate; and
monitoring the flow of oxygen.
Additionally an automatic blockage test is performed by closing off all the valves except for the valve or valves in one gas path through the reactor vessel and delivering a gas at a pre-set flow rate and pressure through said gas path and monitoring the gas throughput.
Further the invention provides an ozone hydroxyl radical analyser of the type comprising:
a reactor vessel having inlets and outlets;
a sampling device connected to the reactor vessel;
a base liquid tank connected to the reactor vessel;
an acid tank connected to the reactor vessel;
an ozone generator feeding the reactor vessel;
associated pumps and valves;
a control and measurement unit; and
the reactor vessel includes a plurality of beads of an inert material.
In one embodiment of the invention the inert material is glass.
The beads are substantially spherical having a diameter of between 1 mm and 10 mm and preferably between 2.5 mm and 3.5 mm.
In one embodiment the ozone generator and the acid tank feed a common inlet to the reactor vessel.
The reactor vessel is constructed so that it has a liquid outlet at its lowermost position and in which all sources of the reactor vessel slope downwards to the liquid outlet to ensure the smooth flow of liquid out of the reactor vessel.
Preferably the reactor vessel is formed from a weldable fluorocarbon which can be chosen from perfluoroalkoxy (PFA), polyvinylidine fluoride (PVDF) and fluorinated ethylene propylene (FEP).
A particularly preferable construction of ozone generator is of concentric tube type wherein the inner and outer walls of the tube form an annular gap through which oxygen containing gas flows between an outer tubular electrode and an inner tubular electrode which is applied to the innermost surface, the interior of the tube being filled with a sealant.
Preferably the sealant is silicon rubber.
An ideal construction of ozone generator is one manufactured from a leaded glass.